Electronic equipment often employs printed circuit boards or cards. These cards typically are mounted in a chassis or card rack by stacking the cards in row alignment with one another. Row alignment in the chassis is defined by slotted or spaced surfaces within or on the chassis, with each circuit board placed in a slot or between a pair of spaced surfaces. A retainer may be provided in the chassis slot to captivate a card positioned therein. Many applications for such retainers require high performance that will captivate a printed circuit board under the most extreme shock and vibration conditions such as those encountered by spacecraft or military aircraft.
Typical printed circuit board retainers are described in U.S. Pat. Nos. 4,823,951 and 5,036,428, the teachings of which are incorporated herein by reference. Such retainers comprise a partially threaded screw or rod and a plurality of members slideably mounted in an end-to-end relationship on the rod. The members disposed on the rod have wedge-shaped end portions which are engagable with one another. The wedge-shaped end portions serve to move at least one of the members in a transverse direction relative to the rod when the members are moved towards one another along the rod. Such movement may be achieved by providing the rod with screw threads to engage and move the distal-most member when the rod is rotated. Alternatively, the movement may result from the action of a lever assembly used to draw the rod away from the distal-most member, thereby pulling that member toward its companions.
Commonly, the rod in prior art retainers is threaded at one end to engage with mating threads on a nut attached to the end-most sliding member mounted on the rod. The opposite end of the rod includes a portion that may be engaged by a tool to allow the rod to be rotated. In so doing, the members are moved toward one another as the threaded rod is rotated in the tightening direction.
The transverse direction in which the member is moved acts to engage a clamping surface of that member against an edge of the printed circuit board. The opposite edge of the board is thereby forced into contact with, and clamped against, a spaced surface fixedly connected to or integral with the chassis in which the board is to be mounted. Typically, the spaced surface fixedly connected to the chassis is the wall of a housing that is screwed or rivetted to the chassis.
The housings of the prior art are mounted (e.g., rivetted or screwed) to the chassis during the manufacture process, or more commonly, by the end user during the application. If the housing is to be mounted by the end user, the retainers and housings are shipped unassembled, although these components can be shipped assembled with instructions to remove the retainer from the housing before mounting the housing to the chassis. Following attachment of the housing to the chassis, the end user must re-assemble the retainer in the housing by inserting a first end of the retainer rod through an opening in a housing end wall, positioning the slideable members on the rod, screwing the first rod end into a nut attached to the end-most sliding member mounted on the rod, and passing the first rod end through a second housing end wall opening.
After mounting the housing and re-assembling the retainer, the end user must install the circuit board between the retainer and a housing side wall. Because it is desirable to maximize the number of circuit boards held in the chassis, retainer housings are designed with a minimum distance between each pair of side walls. As a result, insertion of the circuit board into the space between the retainer and one of the side walls is hampered or prevented if the retainer members are not maintained in proper alignment on the rod. Further, the use of excessive force to install the circuit board between the retainer and housing side wall causes excessive wear and tear on the retainer and the circuit board and may cause breaking of the circuit board. Such misalignment may occur, for example, by rotation of the members on the rod when the retainer is in a relaxed position. One approach to solving the problem of misalignment has been to provide a spring bias, such as that disclosed in U.S. Pat. No. 4,823,951, between the rod and the slideable member, the bias being provided by a leaf spring mounted on at least one of the slideable members.
A need therefore exists for a retainer assembly which eliminates or substantially reduces the labor-intensive, time-consuming process for mounting the retainer to a chassis. The improved retainer would facilitate initial installation, inspection, repair and/or replacement of the slideable members on the retainer rod and would also facilitate installation of the board between the retainer and a side wall of the housing.